The present invention relates generally to Electro Active Polymers (EAP) that convert between electrical energy and mechanical energy. More particularly, the present invention relates to EAP polymers and their use in energy conversion devices that convert between thermal, mechanical, and electrical energy from thermal energy sources such as combustion.
In many applications, it is desirable to convert between electrical energy and mechanical energy. Exemplary applications requiring translation from electrical to mechanical energy include robotics, pumps, speakers, general automation, disk drives and prosthetic devices. These applications include one or more actuators that convert electrical energy into mechanical workxe2x80x94on a macroscopic or microscopic level. Common electric actuator technologies, such as electromagnetic motors and solenoids, are not suitable for many of these applications, e.g., when the required device size is small (e.g., micro or mesoscale machines). These applications include one or more transducers that convert mechanical energy into electrical energy. Common electric generator technologies, such as electromagnetic generators, are also not suitable for many of these applications, e.g., when the required device size is small. These technologies are also not ideal when a large number of devices must be integrated into a single structure or under various performance conditions such as when high power density output is required at relatively low frequencies.
Several xe2x80x98smart materialsxe2x80x99 have been used to convert between electrical and mechanical energy with limited success. These smart materials include piezoelectric ceramics, shape memory alloys and magnetostrictive materials. However, each smart material has a number of limitations that prevent its broad usage. Certain piezoelectric ceramics, such as lead zirconium titanate (PZT), have been used to convert electrical to mechanical energy. While having suitable efficiency for a few applications, these piezoelectric ceramics are typically limited to a strain below about 1.6 percent and are often not suitable for applications requiring greater strains than this. In addition, the high density of these materials often eliminates them from applications requiring low weight. Irradiated polyvinylidene difluoride (PVDF) when combined with various copolymers is an electroactive polymer reported to have a strain of up to 4 percent when converting from electrical to mechanical energy. Similar to the piezoelectric ceramics, the PVDF-based material is often not suitable for applications requiring strains greater than 4 percent. Shape memory alloys, such as nitinol, are capable of large strains and force outputs. These shape memory alloys have been limited from broad use by unacceptable energy efficiency, poor response time and prohibitive cost.
In addition to the performance limitations of piezoelectric ceramics and irradiated PVDF-based materials, their fabrication often presents a barrier to acceptability. Single crystal piezoelectric ceramics must be grown at high temperatures coupled with a very slow cooling down process. Irradiated PVDF-based materials must be exposed to an electron beam for processing. Both these processes are expensive and complex and may limit acceptability of these materials.
As advances in microchip fabrication continue to reduce the cost and the size of logic devices while increasing their computing capabilities, new portable electronic devices using these logic devices are continually being developed. Also, these logic devices are being incorporated into existing electronic devices to increase their functionality and in some case to enable portability. Cellular phones, pagers, personal digital assistants, MP-3 players, navigational devices and locator devices are a few examples of newer portable electronic devices. These portable electronic devices along with other older portable electronic devices such as flashlights, electric tools, credit card readers and radios are utilized in many activities. All of these devices require a source of electrical energy to operate. Typically, the devices employ disposable or rechargeable batteries as an electrical power source. Performance parameters of the batteries such as cost, weight and life-time are critical element in the design and operation of these devices. In other applications, light-weight power sources are needed to power newer portable electronic devices such as minirobots and microrobots and micro-air vehicles that may be used for surveying and reconnaissance for civilian and military application. For these devices, power to weight ratios are a critical consideration.
With the portable electronics devices describe above, it would be desirable to provide portable energy sources with a high power to weight ratio that generate power over a significant time period. Hydrocarbon based fuels have a relatively high energy density as compared to batteries. For instance, the energy density of a hydrocarbon based fuel may be 20 times higher than a density of a battery. Thermo-electromechanical power generation systems that utilize a thermodynamic process such as combustion to generate mechanical energy which is converted to electricity are well known in the art. For instance, a cellular phone may be powered from a generator connected to an automobile engine. However, traditional combustion-driven thermo-electromechanical power generation systems with a reasonable high power to weight ratio tend to be quite heavy and relatively non-portable. At smaller scales, e.g. lower weights, the power to weight ratio of these systems rapidly decreases. Thus, batteries are used as the power source in most portable electronic devices. In view of the foregoing, alternative light-weight, scaleable devices that efficiently convert thermally generated mechanical energy to electrical energy would be desirable.
This invention addresses the needs indicated above by providing generators with one or more transducers that use electroactive polymer films to convert thermally generated mechanical energy to electrical energy. The generators may include one or more transmission mechanisms that convert a portion of thermal energy generated from a heat source such as internal combustion, external combustion, solar energy, geothermal energy or waste heat, to mechanical energy that is used to drive the one or more transducers located in the generator. The energy received by the transducers may be converted to electrical energy by the transducers in conjunction with conditioning electronics located within the generator. One embodiment of the present invention provides an energy conversion device with two chambers, each chamber including a diaphragm transducer that may convert thermal energy to electricity using a thermodynamic cycle such as a Stirling gas cycle. The thermodynamic cycle of the energy conversion device may be reversed to provide cooling to an external device such as a semiconductor device.
One aspect of the present invention provides a generator for converting thermal energy to electrical energy. The generator may be generally characterized as including: 1) one or more transducers where each transducer comprises at least two electrodes and a polymer arranged in a manner which causes a change in electric field in response to a deflection applied to a portion of the polymer; 2) conditioning electronics connected to the at least two electrodes and designed or configured to add and remove electrical energy from the transducer; and 3) one or more transmission mechanisms designed or configured to receive thermal energy and to convert a portion of the thermal energy to mechanical energy, where the mechanical energy results in a deflection in the portion of the polymer. The transmission may convert thermal to mechanical energy using a gas. The gas may be generated from a boiling liquid as in a steam cycle, or it may be intrinsically a gas throughout the cycle. The gas may comprise one of helium, nitrogen, carbon dioxide, air, water, hydrocarbons, and halogenated hydrocarbons. A housing may enclose the one or more transducers, the conditioning electronics and the one or more transmission mechanisms.
In specific embodiments, the one or more transmission mechanisms may transfer the portion of the thermal energy via a mechanical linkage or the thermal energy may be converted to mechanical energy via a gas expansion. The one or more transmission mechanisms may comprise a hydraulic fluid where the hydraulic fluid is a boilable liquid. The one or more transmission mechanisms may comprises a heat exchange mechanism where the heat exchange mechanism transfers thermal energy via heat conduction, heat convection, radiation heat transfer or combinations thereof. The thermal energy received by the one or more transmission mechanisms may be solar energy or excess energy from an engine block.
In particular embodiments, the generator may include a combustion chamber for combustion of a fuel. The fuel may be a liquid fuel, a gaseous fuel, a gel fuel a solid fuel selected from the group consisting essentially of propane, butane, natural gas, hydrogen, kerosene, and gasoline. In addition, the combustion chamber may include 1) at least one fuel inlet for injecting the fuel into the combustion chamber and at least one exhaust outlet for ejecting a combustion product gas mixture from the combustion chamber, 2) a storage chamber for storing the fuel, 3) a pump for moving the fuel from the storage chamber to the combustion where the pump includes an electroactive polymer transducer, 4) a pump for moving external air to the combustion chamber where the pump includes an electroactive polymer transducer, and 5) an ignition device for initiating combustion in the combustion chamber.
In other embodiments, a portion of a surface bounding the combustion chamber may be the polymer where the combustion of the fuel results in a gas expansion, the gas expansion produces the deflection of the polymer portion of the surface bounding the combustion chamber. The polymer portion of the surface bounding the combustion chamber may expand to form one of a balloon-like shape, a hemispherical shape, cylinder shape, or a half-cylinder shape. A portion of a surface bounding the combustion chamber may be a piston where the combustion of the fuel moves the piston to generate mechanical energy.
In particular embodiments, the conditioning electronics may be designed or configured to perform one or more of the following functions: voltage step-up, voltage step-down and charge control where charge is added to, or removed from, the polymer using the charge control. The generator may also include 1) an electrical interface designed or configured to output the electrical energy, 2) one or more batteries designed or configured to store electrical energy removed from the one or more transducers, 3) one or more batteries used to increase the charge of the polymer and 4) a logic device where the logic device is designed or configured to control an addition of charge, a deletion of charge or a combination thereof on the polymer. The generator may also include one or more sensors connected to the generator where at least one of the one or more sensors is designed or configured to monitor a temperature or to monitor a pressure and where at least one of the one or more sensors is designed or configured to monitor at least one of the following quantities: the deflection in the portion of the polymer, a voltage in the portion of the polymer or a charge in the portion of the polymer.
Another aspect of the present invention may provide a generator for converting thermal energy to electrical energy. The generator may generally be characterized as including: 1) one or more transducer where each transducer may comprise at least two electrodes and a polymer arranged in a manner which causes a change in electric field in response to a deflection applied to a portion of the polymer; and 2) charge control circuitry connected to the at least two electrodes and designed or configured to remove electrical energy from the one or more transducers. The charge control circuitry may be designed to add charge to the one or more transducers. Further, the generator may also include a logic device where the logic device is designed or configured to determine an amount of charge to add or to delete from the polymer.
In particular embodiments, the generator may include: 1) step-down circuitry designed or configured to receive an input signal with an input voltage level and output an output signal with an output voltage level where the output voltage level is lower than the input voltage, 2) an electrical output interface designed or configured to output the output signal where the electrical output interface is connected to a battery, 3) one or more power conversion circuitry units and 4) one or more capacitors designed or configured to reduce a voltage level of a signal received by the one or more power conversion circuitry units. The output voltage level may be between about 3 Volts and about 400 Volts.
In particular embodiments, the step up circuitry may be designed or configured to receive an input signal with an input voltage level and output an output signal with an output voltage level where the input voltage level is lower than the output voltage level where the output signal is received by the charge control circuitry. The step-up circuitry may include an electrical input interface designed or configured to receive an input signal where the electrical input interface is connected to a battery. A voltage of the battery may be between about 1.5 and about 48 Volts.
Another aspect of the present invention provides an electroactive polymer energy conversion device for converting between thermal energy and electrical energy, the energy conversion device may be characterized as including: 1) two or more transducers where each transducer comprises at least two electrodes and a polymer arranged in a manner which causes a change in electric field in response to a deflection applied to a portion of the polymer; 2) two chambers enclosing a volume of a working fluid distributed between the chambers where the two chambers comprise: i) a first chamber with a first transducer and a first portion of the working fluid enclosed by the first chamber and ii) a second chamber with a second transducer and a second portion of the working fluid enclosed by the second chamber; 3) conditioning electronics connected to the at least two electrodes in each transducer and designed or configured to apply a charge to the transducers; and 4) one or more transmission mechanisms designed or configured to receive thermal energy.
In particular embodiments, the energy conversion device may also include: 1) a flow conduit designed or configured to allow the working fluid to flow between the first chamber and the second chamber, where the flow conduit may be designed or configured to have negligible heat transfer with the working fluid, or have significant heat transfer to affect thermal behavior of the working fluid as in a regenerator, 2) an insulation barrier designed or configured to minimize heat transfer between the first chamber and the second chamber, 3) a housing enclosing the two or more transducers, the two chambers, the conditioning electronics and the one or more transmission mechanisms and 4) an insulation layer attached to the polymer where the insulation layer is designed or configured to reduce heat transfer to the polymer where the insulation layer comprises one or more of a plurality of passive polymer layers, compliant inorganic materials, wetting liquids and combinations thereof.
In particular embodiments, the working fluid in the first chamber may be maintained at about a first temperature and the working fluid in the second chamber may be maintained at about a second temperature. The two or more transducers, the first chamber, the second chamber, the conditioning electronics and the one or more transmission mechanisms may be fabricated on a semiconductor, insulating, or metal substrate or a substrate made from combinations thereof. The energy conversion device may also include an insert located within the first chamber designed or configured to substantially conform to a contracted shape of the polymer of the first transducer and an insert located within the second chamber designed or configured to substantially conform to a contracted shape of the polymer of the second transducer.
In other embodiments, the thermal energy may be applied to the working fluid in the first chamber to expand the working fluid where the expansion of the working fluid deflects the polymer in the first chamber. The working fluid in the first chamber may be transferred to the second chamber via a flow conduit where the total volume of the working fluid in the first chamber, the second chamber and the flow conduit during the transfer remains substantially constant. The working fluid in the second chamber may be compressed at substantially constant temperature to cause heat to flow from the working fluid.
In other embodiments, the first transmission mechanism may be designed or configured to receive thermal energy and transfer a portion of thermal energy to the first chamber where the first transmission mechanism transfers the portion of the thermal energy via a fluid. The first transmission mechanism may receive thermal energy generated from an external heat source where the external heat comprises one of a solar heat source, an external combustion heat source, and a waste heat source. The first transmission mechanism may include a heat exchange mechanism where the heat exchange mechanism transfers a portion of thermal energy via at least one of heat conduction, heat convection, and radiation heat transfer.
In yet other embodiments, the polymer in the first chamber may be contracted to compress the working fluid in the first chamber where a portion of thermal energy generated during the compression of the working fluid in the first chamber is transferred from the working fluid via a heat exchanger. The working fluid may be a refrigerant of some type. The working fluid in the first chamber may be transferred to the second chamber via a flow conduit where a total volume of the working fluid in the first chamber, the second chamber and the flow conduit during the transfer remains substantially constant. The working fluid in the second chamber may be expanded resulting in working fluid cooling and heat transfer from the second chamber into the working fluid. The compression of the working fluid may convert a portion the working fluid to a liquid. The energy conversion device may include a first transmission mechanism designed or configured to cool an external device where the external device is a semiconductor device.
These and other features and advantages of the present invention will be described in the following description of the invention and associated figures.